1. Field of the Invention
The present invention relates to a method for arranging print head chips, and particularly relates to a method of arranging print head chips using a single arrangement start point in order to obtain a print head with high print quality.
2. Description of the Related Art
In the typical printer technology, a laser is used as a light source in a printer head to scan and transfer the printing information as light signals to a rotating drum in order to generate electrostatic latent images formed on the rotating drum. Moreover, the printing method further includes a toner absorbing step, a transferring step, a hot pressing step, an electrostatic discharging step etc. to achieve printing requirement. However, a laser printer head of the prior art has many optical components, and the mechanism of the laser printer head is complex and the optical path of the laser printer head is very longer. Hence, the optical structure is quite complex and difficult to reduce in size for using a laser in this way. Therefore, the current trend is toward using light emitting diodes to replace lasers as the light sources in printer heads, which can simplify the optical structure.
For example, a printer resolution is 600 dpi (dots per inch) on A4 size paper. A PCB has 39 LED array chips and 39 drive ICs, and each LED array chip has 128 LED spots (an LED spot is the light emitting portion of an LED). Hence, there are 4992 LED spots on the PCB to comprise a printing width of 211 mm.
A further requirement is to reduce the volume of each light emitting diode so as to increase the printer resolution. The number of light emitting diodes per unit area in the printer head can be increased when the volume of each light emitting diode is reduced. Because the yield rate of LED array chips is increased, 26 LED array chips and 26 drive ICs are applied on the PCB. Each LED array chip has 192 LED spots. Hence, there are 4992 LED spots on the PCB to comprise a printing width of 211 mm, too.
Moreover, according to the typical packaging method, a highly precise packaging apparatus is required to arrange the light emitting diode arrays and the driver integrated circuits so that they are exactly parallel to each other in a printed circuit board. Then, a wire bonding process is performed to form about 5000 wires between the light emitting diode arrays and the driver integrated circuits if the printer resolution is 600 dpi (dots per inch) on A4 size paper. The driver integrated circuits drive the light emitting diode arrays through these wires.
FIG. 1 shows a flowchart of a method for arranging print head chips on a PCB according to the prior art. For example, if the 26 LED array chips is used, the method for arranging print head chips includes:
Step S100: setting a fiducial mark as a reference fiducial point on a PCB for arranging a first LED array chip on the PCB;
Step S102: taking a position of a last LED spot of the first LED array chip as another reference fiducial point for arranging a second LED array chip adjacent to the first LED array chip on the PCB; and
Step S104: repeating step S102, taking a position of a last LED spot of a last LED array chip as another reference fiducial point for arranging a next LED array chip adjacent to the last LED array chip on the PCB. In other words, the LED array chips are arranged on the PCB in sequence.
FIG. 2 shows a schematic view of offsets of LED spots arranged along an x-direction and a y-direction according to the prior art. There are two problems when using the printer resolution is 600 dpi (dots per inch) on A4 size paper, as following:
1. An offset along an x-direction between the first LED spot d1a on a substrate ba and a last LED spot d192a on the substrate ba is about 211 μm±300 μm. In other words, a maximum offset Xn along the x-direction between the first LED spot d1a and the last LED spot d192a is 300 μm. In addition, with regard to the prior art with the size of A4 and the resolution of 600 dpi, a distance of each spot is about 42.3 cm. Hence, the distance of the maximum offset Xn along the x-direction is about 7 spot (300/42.3=7.09) in the prior art.
2. A maximum offset Yn along a y-direction between the first LED spot d1a on the substrate ba and the last LED spot d192a on the substrate ba is 150 μm. In addition, with regard to the prior art with the size of A4 and the resolution of 600 dpi, a distance of each spot is about 42.3 μm. Hence, the distance of the maximum offset Yn along the y-direction is about 3.5 spot (150/42.3=3.54) in the first embodiment.
In order to solve the problems of offset along x-direction and y-direction, it is necessary to do position compensation for satisfying the print need of accurate color trap. The method for solving the problems includes following two method:
First method includes: firstly, measuring the 4992 LED spots to obtain x and y coordinate positions or measuring the 4992 LED spots and using a semiconductor laser amplifier (SLA) to obtain imaged x and y coordinate positions; and then calculating the offset of the 4992 LED spots and proceeding printing data shift.
Second method includes: firstly, decreasing measurement points of the 4992 LED spots; and then calculating a formula to do curve fitting via the measured data in order to obtain another formula with good linearity.
However, no matter which solve method is used in the prior art, abovementioned steps such as measuring LED spots and position compensation and the follow-up step of printing test and verifying print quality need to pay large cost.